T L a a k ke la M o r r is o n L a k e H a La u k te e te Hearne Hill East Hautete Lake H a tc h e r y A r m Natowite B a Old Fort Lake L b a in Mountain ke e Smithers Landing Nizik McKendrick Lake Island Ba b in e L H a a g a k n e A r m Ministry of Employment and Investment Energy and Minerals Division Geological Survey Branch TILL GEOCHEMISTRY OF THE OLD FORT MOUNTAIN MAP AREA, CENTRAL BRITISH COLUMBIA (NTS 93Ml1) By Victor M. Levson, Stephen J. Cook, Jennifer Hobday, Dave H. Huntley, Erin K. O'Brien, Andrew J. Stumpf and Gordon Weary OPEN FILE 1997- 1Oa INTRODUCTION - - - - This paper describes selected results of a till in low-lying drift-covered regions of the northern Interior geochemical sampling program conducted in the Old Fort Plateau. For example, prior till and lake sediment Mountain map area (NTS 93 M/1) by the British geochemistry surveys in the Nechako River map ania Columbia Geological Survey as part of a comprehensive (NTS 93F) to the south were successful in delineating survey of the entire Babine copper porphyry belt. The several areas of known mineralization (Cook et al., 1995; results of complimentary lake sediment geochemistry ad Levson and Giles, 1997) and in revealing locations of new bedrock geology mapping progms are presented by Cook mineralized zones. For this reason, till geochemical et al. (1997%b) and MacIntyre et al. (1997%b in pocket), studies in the Babine porphyry belt have been conducted in respectively. The surficial geology of the map area was conjunction with ongoing bedrock geology mapping provided by Huntley et al. (1996). The geochemical data (MacIntyre et al., 1997% b), surficial geology mapping discussed in this paper has previously been presented in a (Levson et al., 1997a) and regional lake sediment digital format (Levson et al., 1997a). Complete till geochemistry (Cook et al., 1997% b) components. These geochemistry results for the entire Babine copper porphyry studies are part of the Nechako National Mapping belt will be provided in an upcoming publication. (NATMAP) Project, a joint project of the British am Columbia Geological Survey Branch, the Geological The map occurs at the northern end of the Survey of Canada and university researchers. Nechako Plateau in the Babine Lake region and covers the central part of the Babine porphyry belt. Copper porphyry mineralization in the study area is hosted in Eocene Babine intrusives. Major deposits include the former Bell DESCRIPTION OF SURVEY AREA and Granisle copper mines. Porphyry copper deposits remain the primary exploration target in this region ad The Old Fort Mountain map area lies at the northern several active !porphyry properties, including the Hearne end of the Nechako Plateau, in the west-central part of the Hill prospect, are within the bounds of the map area. Interior Plateau (Holland, 1976). Physiographically, the The purpose of the regional till geochemistry map area is dominated by a low mountain range that program is to improve the existing geochemical dabbase trends southeasterly through the centre of the map area and of the area. This information will help to better assess the by the adjacent Babine Lake valley. The dominant feature mineral potential of the region and thus increase the in the highest mountain in the area is Old Fort Mountain possibility of new discoveries. The Nechako Plateau is (1570 m), rising above lake level at about 712 metres ch;ll.actexized by subdued topography, an extensive driR above sea level. Other peaks in the area include Hearne cover and poor bedrock exposure which have hided Hill (1370 m) in the north-centml part of the map sheet mineral exploration in the Babine porphyry belt. Results and Wedge Mountain (1250 m) in the northeast comer, of the till geochemical survey are expected to provide adjacent to the Northwest Arm of Takla Lake. useful new data to stimulate further exploration. Well developed flutings and drwnlinoid ridges, Two approaches to till geochemical studies in the oriented roughly parallel to the Babine Lake valley, are Babine porphyry belt have been employed by the British dominant features in the area. In low-lying regions large Columbia Geological Survey: 1) regional geochemical glacial lakes formed and deposited extensive belts of surveys to identify geochemically anomalous sites for glaciolacustrine sediments, generally below 950 metres follow-up by the mineral exploration industry and 2) elevation. Topography in these areas is subdued and olb detailed investigations around areas of known glacial landforms are often difficult to recognize. mineralization to evaluate the effects of surficial processes on geochemical distribution patterns, refine models of glacial dispersal in montane and plateau areas and develop methods of drift exploration applicable to the Interior PREVIOUS WORK Plateau. Surficial geology mapping was also conducted in conjunction with till geochemical sampling in arch to The surficial geology of the this part of the Babine understand the glacial history of the area and provide a porphyry belt was discussed by Huntley et al. (1996) and basis for design of anomaly follow-up programs. Levson et al. (1997~). Wittneben (1981) completed Stratigraphic and sedimentologic studies of Quaternary 150 000 scale terrain mapping in parts of the Hazelton deposits are also included in order to define the glacial map sheet (NTS 93 MJNW, NE, SW). Tipper (1971) ad history and aid in interpreting till geochemical data. Plouffe (1994, 1996) completed reconnaissance mapping i of Quaternary deposits south and west of the Babine area Regional till and lake sediment gexhemical surveys in other parts of the Nechako Plateau. A summary of and bedrock and surficial geology mapping programs have 1:50,000 scale surficial geology mapping, conducted as proven highly effective in stimulating mineral exploration part of the NATMAP and Interior Plateau programs, was Open File 1997-10a provided by Levson and Giles (1997). Nine regional of the NATMAP and Interior Plateau programs (Levson (150 000-scale) surficial geology maps have been and Giles, 1995, 1997; O'Brien et al., 1995; O'Brien, published as part of this work throughout the Nechako 1996; Stumpf et al., 1996, 1997). An overview of drift Plateau. prospecting methods and research of particular relevance to the Interior Plateau region was completed by Kerr ax# Till geochemical studies in the Babine region wae Levson (19971, A discussion of aarent methods of Levson et (1997a)* Recent exploration in he southem Ne&&o Plateau ;sea, typical geochemical studies elsewhere in the Necbako Plateau problems encwnkred and that can be used to were dkUssed Levson and "la (IB7)* as kVelopand ref= drift explodon methods, was provided study investigations have been conducted to date, part by Levson and Gila (1997). FIELD AND LABORATORY PROCEDURES horizons, local slope, bedrock striae, bedrock lithology, clast provenance and abundance of mineraked emtics. FIELD METHODS Sedimentologic data for each of the sampled deposits are provided in Appendix A together with summary Surficial geology mapping was completed by descriptions of the sample site and other relevant data. interpretation of air photographs, field checking existing terrain map data and stratigraphic and sedimentologic studies of Quaternary exposures in the map area. Ice-flow LABORATORY METHODS AND history for the map area was largely decipM from the QUALITY CONTROL study of crag-and-tail features, flutings, drumlins, striae and till fabric data. Till samples collected during the regional geochemical survey (each 3-5 kg in weight) are air d&d, Till samples were collected for geochemical analysis p). in o& to locate glacially dispersed metallic minerals in split and sieved to -230 mesh (<62.5 One split from each sample was reserved for grain size or other follow-up the region. Sample sites were selected to provide as complete a coverage of the map area as possible using analyses. The -230 mesh fraction from each sample was existing access routes. Sample sites consisted of natural analyzed by instrumental neutron activation analysis and man-made exposures (roadcuts, borrow pits, soil pits (INAA) for 35 elements at Activation Laboratories Ltd. in and trenches). Field sites were marked with metal tags and ~nc&ter,Ontario and by inductively coupled plasma flagging tape. Locations of samples sites wen? plotted on analysis (ICP) after aqua regia digestion for 30 elements, at Acme Analytical Laboratories Ltd. in Vancouver, a 150 000 topographic base map with the aid of air British Columbia. For the ICP analysis, a 0.5 gram photographs md a Geographic Positioning System. Each till sample site is shown with an x on the accompanying sample is digested with 3 millilitres of 3-1-2 HCL-HN03- bedrock geology map (MacIntyre et al., 1997b, in pocket). H20 for one hour and diluted to 10 millilitres with water. A numbered sample location map is provided as an This leach is partial for Mn, Fe, Sr, Ca, P, La, Cr, Mg, overlay and in Appendix A together with UTM Ba, Ti, B and W and limited for Na, K and Al. Mercury coordinates for each sample site. analysis was by flameless AA. A total of 287 regional till samples were collected in Distribution maps for gold, arsenic, antimony, iron, the study area at an average density of approximately one copper, zinc, lead, silver, molybdenum and mercury at.e sample per 3 square kilometres. Higher density sampling provided in Appendix A. Maps for remaining elements was in of perceived higher mineral will be given at a later release for the entire Babine conducted areas porphyry belt. Analytical results for all 287 samples potential and around known mineral prospects, to provide included in the regional data set are also provided in a clearer understanding of glacial dispersal processes.